Deformable wall tuning of resonant cavities for electron discharge tubes



g- 2, 1965 J. R. BAGNALL 3,

DEFORMABLE WALL TUNING OF RESQNANT CAVITIES FOR ELECTRON DISCHARGE TUBES Filed July 5, 1962 INVENTOR 01m W6 BY a:

ATTORNEY-5 United States Patent 3,264,513 DEFORMABLE WALL TUNING 0F RESONANT CAVITIES FOR ELECTRON DISCHARGE TUBES .Iohn Ralph Bagnall, Chelmsford, England, assignor to English Electric Valve Company Limited, London, England, a British company Filed July 5, 1962, Ser. No. 207,546 Claims priority, application Great Britain, Sept. 6, 1961,

1 Claim. (Cl. 315--5.22)

3,264,? 13 Patented August 2, 1966 ice third wall which is of tubular form. At least .a portion necessary to an understanding thereof,.one form of tunable resonant cavity in accordance with this invention and suitable for use in a klystron; and FIGURES 4 and 5 are views of the same nature as-FIGURES 2 and 3 respectively, showing another embodiment of the invention.

FIGURE 1 illustrates the so-called cylindrical reentrant type of resonant cavity commonly employed in integral resonant cavity klystrons at the present time. Such klystrons may, of course, have one or more such cavities. The cavity proper is the unshaded space 1 within the metal walls represented in FIGURE 1 by the externally cross-hatched line bounding the space. As will be seen there is a central upstanding so-called post 2, the top of which faces the top wall 3 which is substantially parallel to and fairly close to the top of the post, the wall 3 being also substantially parallel to, but at a considerably greater distance from, the annular bottom wall 4 round the bottom of the post. The cavity thus formed is, in section, roughly dumb-bell shaped. It is common to provide for tuning a klystron resonant cavity by varying its axial dimensions and, at present, this is normally done by making one or the other of the opposite substantially parallel walls of the cavity in the form of a thin flexible metal diaphragm and providing a screw or other device to deform the flexible wall in question towards or away from the opposite wall. Thus, in the case of a cavity as illustrated by FIGURE 1, current practice would be to constitute the wall 3 or the wall 4 by a thin flexible metal diaphragm and to provide a screw or the like (not shown) to deform the diaphragm so as to vary, for tuning purposes, the separating gap between the wall 3 and the adjacent top of the post 2.

The amount of variation of separating gap required for tuning purposes is very small. Thus, to quote typical practical figures, a change of 0.001" in the separating gap of a cavity as represented by FIGURE 1 is sulficient to produce a change of somewhere about 200 to 250 mc./ s. in the resonant frequency of a cavity designed for operation at about 10,000 mc./s. Accordingly, known tunable resonant cavities of the type described, wherein one of the cavity walls is constituted by a flexible diaphragm, have the serious defect that ambient temperature changes, ambient pressure changes, vibration and other more or less random extraneous causes are apt to produce undesired movements of the diaphragm big enough to result in material undesired changes in resonant frequency. The present invention seeks to avoid this defect.

According to this invention the walls of a tunable resonant cavity suitable for use in a klystron or like electron discharge tube include two mutually spaced walls connected together and spaced from one another by a of said third wall is deformable to vary its length and therefore to vary the separating distance between said two mutually spaced walls. By deforming the tubular wall to vary its length, the separating distance between the said two mutually spaced walls, and therefore the resonant frequency of the cavity, may be varied.

Preferably, though not necessarily, the tubular wall is circular in shape and the two mutually spaced walls are circular, one of the latter walls comprising an annular portion and a central post portion, the top of which is fairly close to the other wall.

Preferably the tubular wall is caused to be deformable by constructing it with at least one convolution or bellows-like bend in its length, means being provided for deforming'said bend or convolution to vary the overall length of the whole tubular wall.

In one way of carrying out the invention, the means for deforming the'tubular wall comprise means for varying its length symmetrically with respect to the axis so that, in any position of :adjustmenL-the length of said tubular wall, measured along lines parallel to the axis, is the same for all such lines. In another way of carrying out the invention, however, the adjustment of length is asymmetrical, the length of thetubular wall at one place round the periphery being fixed and means being provided for deforming said wall to vary the length elsewhere.

Because variation of the resonant frequency is obtained by deforming a tubular wall to vary its length and thereby to vary the distance between two other walls joined by said tubular wall and co-operating therewith to form the cavity, and because neither of said two other walls is constituted by a diaphragm or is flexible in the ordinary sense of that word, there is good precise control of frequency adjustment and much greater immunity from undesired frequency variation due to ambient temperature and pressure variation, or to vibration, than is the case with the usual known structures of the diaphragm wall type. The deforming means may comprise screws or bolts symmetrically arranged round the tubular wall in the case of axially symmetrical adjustment of length or one screw or bolt in the case of axially asymmetrical adjustment of length.

FIGURES 2 and 3 show an embodiment, illustrated as applied to a klystron cavity with a waveguide feed to (or from) the cavity wherein the adjustment is axially asymmetrical. Here the space 1 within the cavity is between two transverse metal walls, namely the centrally apertured wall 3 and a wall formed with a central post 2 surrounded by an annular wall member 4. These transverse metal walls are spaced apart along the length of and are brazed to a circular deformable metal tube 5, part of the length of which, between the transverse walls, is formed with a convolution or bellows-like bend 5A which can be deformed to vary the spacing of the transverse walls. There is a hole 6 in the tube 5 for coupling high frequency energy into or out of the cavity and a window plate 7 with a corresponding hole 7A is brazed to the tube 5 so that, at the side where this plate is situated, the length of the tube 5 is rigidly fixed. A waveguide 8 is brazed to the plate 7 and is fitted with a vacuum-retaining mica or glass window (not shown) extending across it to pass high frequency wave energy in accordance with practice known per se. Two lugs 9 and 10 are brazed to the tube 5 near the transverse walls and on the outside of said tube opposite to the location of the plate 7 and waveguide 8. A single screw 11 (shown broken away) fitted with nuts 12 passes through the lugs. As will be apparent, it is possible by means of the screw 11 and nuts 12 to force the lugs 9 and 10 to- 7 3 Wards or away from one the bend SA opposite the waveguide 8 and thus changing another, deforming the part, of

-- tary tubular'wall joining andextendingubeyond said'pair of j V the length of the tube 5 asymmetrically with respecttothe axis. In, this way the separation of the two trans Verse Walls can be varied to vary the resonant frequency. a

The transverse walls are a fixed distance apart on the side adjacent the plate 7 but the separating distance on theopposite side is variable. In one successfully tested structure a as illustrated inFIGURES 2 and 3, the tube 5 was made.

of nickel-iron alloy with 'a wall thicknessof 0.03". This:

structure was found relatively simple and easy to'tune and to berelatively insensitive to normal variationsof ambient temperature and pressure and to vibration and shock.

The modification shown in FIGURESf4and 5 willbe found largely self-explanatory since like references are used for like parts in FIGURES 2 to.5. In FIGURES 4 and 5 two triangular plates 13 'and14 replace the lugs 9 and.10 of FIGURES'Z and 3 and thewindow plate 7 is dispensed with so that the length of the tube is variable in anaxially symmetrical manner. is effected by three symmetrically arranged; screws 15 Such variation fitted With nuts 16 '(thescrews andnuts are not'shovvn in'FIGURES) and connecting the plates 13 and 14 to:

gether. In FIGURES 4 and 5 aco-axialline feed 17 is shown in place of a waveguide.

I claim:

An electron discharge tube having a tunable resonant cavity comprising, a pair of separated rigid walls, a unirigid walls, said vunitary tubular wall including a deform-' ableiportion disposed between'said rigid walls, said :unitary tubularwall having substantially uniform substantial thick-1 ,ness throughout its, length includingflsaid deformable portion, a pair of spaced body portions extending transversely of and connectedto said unitary tubular Wall on opposite sides' of i said. deformable portion, rand means ;adjustably connectedsbetween said pair of spaced body portions and adjustable to applytpressurewtot said deformable portion throughtsaid tubular wall to distort: said deformable .portion to a greater on lesser extent tovary .the distance separating said'rigid' Walls,'thereby varying the resonant frequency of the cavity. t

References Cited by theiE'xaminerp UNITED? STATES PATENTS DAVID; J. GALvI-N; :Primary Examiner; 1

ROBERT SEGAL, ,GEORGE? N UWESTBY, C.

O. GARDNER; Assistant Examiners.. 

